Assign shortcut to Lock Camera to View
Go to User Pereferences/Input tab/3D View/3D View (Global)
There is no entry for "Lock Camera to View", so we will add a new one. 
Click "Add New"
Open the "none" line that was created
In the text field which says "none", type: wm.context_toggle, and press ENTER
A new text field labelled "Context Attributes" appears. Type: space_data.lock_camera, and press ENTER
Define the shortcut. (Some more trial and error could be necessary to find a free one). The shortcut should work already.
Don't forget to also press "Save User Settings" in the User Preferences window.


In the following screenshot I just added the shortcut Ctrl-K:



Also see this blenderartists thread.